Finding an economical means for utilizing solar energy has, of course, become of prime importance in these days of energy shortages. Thus, there is a definite need for inexpensive, lightweight solar collectors which can efficiently transform solar energy into heat energy. Likewise, there is a great need for an inexpensive, lightweight apparatus which is capable of rejecting radiant energy to the atmosphere efficiently. The apparatus of the present invention functions as a solar collector and a radiant energy rejector, and further, can serve as roofing material and insulation for a structure such as a house.
Plain copper sheets with water coils attached thereto have been used as radiant exchangers for both heating and cooling purposes. These copper exchangers have no means to prevent heat loss to the atmosphere by convection. Other than the copper sheeting, traditional solar collectors of many different design types have been used for heating only and have not been intended for use in rejecting radiant energy to the atmosphere. Furthermore, these conventional solar collectors are either of metal or glass design, possibly with a plastic covering, or are made of extruded plastic. These collectors are much heavier and much more expensive than the radiant exchanger of the present invention.
U.S. Pat. No. 4,015,582, Solar Heat Collector, issued to Liu, et al. on Apr. 5, 1977, discloses a solar heat collector comprising a heat insulative base, a layer of heat absorptive material overlying the insulative base, a light transmitting insulating (against convection and infrared losses) protective covering overlying the heat absorptive material to prevent the passage of air into or out of the heat absorptive material, and means for circulating a heat transfer fluid through the collector along one or both sides of the heat absorbing layer. The absorbing surface may be in the form of a black or blackened plate or film or it also can be in the form of a porous medium such as glass fibers, painted metal fibers, or painted screens with high solar absorptivity. The light-transmitting and insulating protective cover can be in the form of glass fiber or it can also be in the form of rigid or flexible plastic foam with entrapped gas bubbles. Since in the present invention the heat transfer takes place within and throughout the heat-absorbing open-celled foam, much better heat transfer can be obtained than by the Liu, et al. invention where most of the heat transfer takes place at the outside surfaces of the heat-absorbing material and only a small amount, if any, of the heat transfer fluid passes through the heat-absorbing material because of the large pressure drop across it. Also, the open-celled foam of the present invention is less expensive and lighter in weight than the materials disclosed in the above patent.
U.S. Pat. Nos. 2,998,005, Solar Heater, and 3,875,925, Solar Heater, issued to Johnston on Aug. 29, 1961 and Apr. 8, 1975, respectively, describe solar collectors which utilize fibrous materials which are probably porous. In Johnston I, a black fiberglass fibrous mat is used to absorb solar energy without any losses due to reflection of the radiant energy. The solar energy is converted to heat in this fibrous mat and the heat is insulated from radiation to the outside by the upper layers of fiberglass. The heat is transferred to air which flows along one surface of the mat. In Johnston II, a porous fibrous material such as fiberglass is used as an outer protective layer. It allows solar energy to pass through to the back wall of the collector where it is absorbed by a black covering, but it does not allow the heat energy to pass back out of the collector. The fibrous materials disclosed in these patents do not allow the easy passage of a heat transfer fluid through them and thus cannot have the advantage of the present invention of being able to have a very large surface area for the transfer of heat to the fluid. Also, the materials disclosed in the two Johnston patents are much more expensive and heavier in weight than the open-celled foam of the present invention.
French publication No. 2,308,882, Solar Heat Trap Using Transparent Multichannel Profile to Accept Radiant and Diffuse Heat Into Dark Packing by Harvey, discloses a solar heat trap collector which is comprised of superimposed transparent channels. The lower channels are filled with fibrous or particulate packing which can absorb heat and transmit it to a heat transfer fluid which is consolidated through both the lower and upper channels. Recirculating the heat transfer fluid over the lower collection level is said to trap collected heat which would otherwise be lost by reflection or reverse radiation. There is no disclosure that this collector can be used to reject radiant energy to the atmosphere. Furthermore, the porous material used in the French publication is very much different from and much harder to handle than the open-celled foam of the present invention.
German Offenlegungsschrift No. 2,719,959, published Nov. 9, 1978, discloses a radiant heat transmitting system in which a radiation absorber with an open structure transmits heat to a gaseous or liquid heat carrier which is contained within the open structure of the absorber. It is stated that the open structure material can be a foamed plastic and polyurethane foam is specifically mentioned. A cover layer of glass or plastic is recommended. Japanese Pat. No. 54-152,241, published Nov. 30, 1979, discloses a heat absorber material for collecting solar energy which comprises an open-celled black synthetic resin foam covered with a transparent outer wall of water-proof resin or glass. The foam is preferably a hydrophilic polyurethane foam. Neither of the above patents disclose or suggest the combination of a gas impermeable layer, an open-celled foam, and a gas reflective layer as a lightweight radiant energy exchanger which is self-supporting and can serve as roofing material and insulation for a structure.
German Offenlegungsschrift No. 2,610,901, published Sept. 29, 1977, U.S. Pat. Nos. 4,143,641 patented Mar. 13, 1979, 4,224,928 patented Sept. 30, 1980, 4,263,896 patented Apr. 28, 1981, 4,266,531 patented May 12, 1981, and 4,271,823 patented June 9, 1981 all show the use of a cover layer of transparent lightweight gas impermeable material having air spaces disposed therewithin. However, none of the above patents disclose the use of such a material with an open-celled foam nor do they disclose or suggest the use of such a material in combination with a foam and a gas impermeable reflective material.